Conductive contact

ABSTRACT

In the electroconductive contact unit of the present invention, a gold plated layer  8  is formed over the surface of an electroconductive needle member  2  via a Ni under layer  7   a , and a layer of iridium (titanium nitride, rhodium or hafnium nitride) is formed on the gold plated layer  8  of the needle portion  2   a  by sputtering, via an Ni under layer  7   b . Thereby, the tip portion is provided with an improved resistance to oxidization and wear without using any special material for the needle member, and the durability of the needle member is improved so that the running cost can be minimized.

TECHNICAL FIELD

[0001] The present invention relates to an electroconductive contactunit for exchanging signals with printed circuit boards, electronicdevices or the likes.

BACKGROUND OF THE INVENTION

[0002] A conventional electroconductive contact unit for use in contactprobes for electrically testing conductor patterns of printed circuitboards and electronic devices typically comprises an electroconductiveneedle member and a tubular holder that receives the needle member in anaxially moveable manner, and the needle member is resiliently urged by acoil spring in the direction to project the tip of the needle memberfrom the front end of the holder so that the tip of the needle membermay be resiliently brought into contact with an object to be tested.

[0003] Silicon wafers and ceramic packages for use with semiconductordevices and glass panels for use in LCD panels are made of materialshaving a relatively high hardness. These components are provided withelectric circuitry, and are subjected to electric testing during themanufacturing process. An electroconductive contact unit (contact probe)is used for such a purpose, and is adapted to establish electric contactwith a part of the circuitry such as a terminal.

[0004] When the object to be tested consists of a component made of ahard material such as those mentioned earlier, and the contact probeuses needle members made of conventional SK material (carbon toolsteel), repeated use of the needle members will result in the wear anddeformation of the contact points in time. As a result, a stable contactresistance may eventually become impossible. Therefore, the needlemembers are required to be replaced in a relatively short period oftime, and this increases the running cost.

SUMMARY OF THE INVENTION

[0005] In view of such problems of the prior art and to provide anelectroconductive contact unit which is resistant to wear and highlydurable, the electroconductive contact unit of the present inventionincludes an electroconductive needle member, and a coil springresiliently urging the needle member in a direction to bring a tipportion of the needle member into contact with an object to becontacted, and is characterized by that: the tip portion of the needlemember is integrally formed with electroconductive material resistant tooxidization and wear.

[0006] Thereby, the tip portion of the needle member can be maderesistant to oxidization and wear, and is prevented from being worn ordeformed even when the object to be tested consists of material having ahigh hardness. Thus, the wear resistance and durability of the needlemember is improved, and a stable contact resistance is ensured.

[0007] In particular, by forming a plating of a highly electroconductivematerial at least on the remaining part of the needle member which isnot integrally formed with the electroconductive material, even when theelectroconductive material does not have an adequately highelectroconductivity owing to a greater weight placed on increasedresistance to oxidization and wear, the electric path between the tipportion of the needle member and the part thereof connected to the coilspring can be plated with highly electroconductive material so that theelectric resistance of the electric path between the needle member andcoil spring can be minimized.

[0008] The electroconductive material may consist of any of iridium,titanium nitride, rhodium and hafnium nitride either by itself or as analloy with gold or platinum. The favorable properties of iridium,titanium nitride, rhodium and hafnium nitride such as a high hardness,resistance to heat and acid and stable contact resistance can be fullytaken advantage of so that the tip portion of the needle member is givenwith an improved wear resistance and durability, and a favorableconductive state (such as a stable contact resistance) can be achievedowing to the stable mechanical contact.

[0009] If the iridium, titanium nitride, rhodium, hafnium nitride oralloy of any one of them with gold or platinum is provided via an underlayer for preventing peeling, the under layer ensures a secureattachment of such material to the needle member even when a directapplication of such material to the needle member would fail to providean adequate force of attachment. Therefore, the electroconductive unitcan be given with a desired wear resistance and durability.

[0010] By using gold for the highly electroconductive material that isplated, even when the electroconductive material does not have anadequately high electroconductivity because of a greater weight placedon increased resistance to oxidization and wear, the needle member maybe given with a high electroconductivity as a whole.

[0011] If the gold plating is formed over the entire surface of theneedle member, and the iridium, titanium nitride, rhodium, hafniumnitride or alloy of any one of them with gold or platinum is providedvia an under layer for preventing peeling, the gold plating that isprovided over the entire surface of the needle member ensures a highelectroconductivity for the needle member as whole, and the under layerensures a strong attachment of the material such as iridium to theneedle member. Also, the gold plated layer under the material such asiridium conducts electricity, and provides an even more favorableelectric property.

[0012] If a gold plating is formed on the outer surface of the iridium,titanium nitride, rhodium, hafnium nitride or alloy of any one of themwith gold or platinum, the material such as iridium improves the wearresistance, and the gold plated layer reduces the electric resistance ofthe needle member as a whole. Even when the gold plated layer is worn ordeformed and the under layer made of such material as iridium isexposed, the presence of the gold plated layer adjacent to such anexposed part helps the electric conductivity of the needle member to bekept high as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Now the present invention is described in the following withreference to the appended drawings, in which:

[0014]FIG. 1 is a vertical sectional view of an electroconductivecontact unit for use in a contact probe embodying the present invention;

[0015]FIG. 2 is a view similar to FIG. 1 showing the contact unitbrought into contact with an object;

[0016]FIG. 3 is an enlarged fragmentary sectional view of the needlemember having an iridium layer coated thereon;

[0017]FIG. 4 is a schematic view showing how the sputtering process isconducted;

[0018]FIGS. 5a, 5 b and 5 c are enlarged fragmentary views showingdifferent shapes of the tip of a needle member;

[0019]FIG. 6 is a view similar to FIG. 3 showing another embodiment ofthe present invention; and

[0020]FIG. 7 is a view similar to FIG. 3 showing yet another embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Preferred embodiments of the present invention are described inthe following with reference to the appended drawings.

[0022]FIG. 1 is a vertical sectional view showing an electroconductivecontact unit 1 for use in a contact probe embodying the presentinvention. This electroconductive contact unit 1 may be used by itself,but is particularly suitable for use in a holder (probe head) of amultipoint contact probe as one of a large number of similarelectroconductive contact units that are arranged one next to another,for instance for a wafer level test. In such a contact probe, the holderis integrally attached to a board mounted on a testing machine via arelay circuit board. The drawing is for illustration purpose only, andthe actual aspect ratio may differ from that of the illustrated example.

[0023] The electroconductive contact unit 1 comprises anelectroconductive needle member 2, a compression coil spring 3 and aholder 4 made of electrically insulating material and defining a largediameter holder hole 4 a and a small diameter holder hole 4 b in acoaxial relationship for receiving the electroconductive needle member 2and compression coil spring 3 therein. The electroconductive needlemember 2 comprises a needle portion 2 a having a pointed end, a flangeportion 2 b provided in the rear end of the needle portion 2 a andhaving a more enlarged diameter than the needle portion 2 a, and a stemportion 2 c projecting from the other end (the lower end in the drawing)of the flange portion 2 b and having a more reduced diameter than theflange portion 2 b. These portions 2 a, 2 b and 2 c are each providedwith a circular cross section, and disposed in a mutually coaxialrelationship.

[0024] The part of the stem portion 2 c of the electroconductive needlemember 2 adjacent to the flange portion 2 b is formed as an enlargeddiameter portion 2 d having a slightly larger diameter than the rest ofthe stem portion 2 c. The enlarged diameter portion 2 d is press fittedinto an end of the compression coil spring 3, and the corresponding coilend thereby resiliently wraps around the enlarged diameter portion 2 d.The electroconductive needle member 2 is connected to the compressioncoil spring 3 in this manner. The connection between the enlargeddiameter portion 2 d and the corresponding end of the compression coilspring 3 can be accomplished not only by the resilient wrappingdescribed above but also by other means such as soldering. In regard tohow the compression coil spring 3 is wound, the one end portionconnected to the enlarged diameter portion 2 d consists of a closelywound portion, and the intermediate portion consists of a coarsely woundportion while the other coil end portion is provided with a closelywound portion 3 a having a prescribed length.

[0025] The small diameter holder hole 4 b of the holder 4 axiallyslidably receives the cylindrical portion of the needle portion 2 a, andthe large diameter holder hole 4 a receives the flange portion 2 b,enlarged diameter portion 2 d, stem portion 2 c and compression coilspring 3. The lower surface of the holder 4 in the drawing is attachedto a relay circuit board 5 which closes the open end of the largediameter holder hole 4 a. The relay circuit board 5 is fixedly attachedto the holder 4 by threaded bolts not shown in the drawing, and isprovided with an internal circuitry 5 a having a terminal surfaceopposing the large diameter holder hole 4 a.

[0026] As shown in the drawing, when the holder 4 and relay circuitboard 5 are assembled to each other, the electroconductive needle member2 is prevented from coming off from the holder hole by the flangeportion 2 b being engaged by a shoulder 4 c defined between the smalldiameter holder hole 4 b and large diameter holder hole 4 a. The axiallength of the large diameter holder hole 4 a is determined in such amanner that the compression coil spring 3 is subjected to a prescribedinitial load by a compressive deformation thereof. The axial lengths ofthe stem portion 2 c and closely wound portion 3 a are determined insuch a manner that the lower end of the stem portion 2 c in the drawingengages the closely wound portion 3 a in the illustrated initial state(prior to the test).

[0027] Referring to FIG. 2, by engaging the tip of the needle member 2 aonto an object to be tested such as a pad 6 a made of Au, Cu or Al andformed on the surface of the wafer 6, an electric signal I istransmitted from the side of the wafer 6 to the relay circuit board 5via the needle member 2 and compression coil spring 3. The signal isthen forwarded to a control system not shown in the drawing via acircuit board not shown in the drawing connected to the relay circuitboard 5, and a desired test can be conducted.

[0028] In the initial state, the stem portion 2 c is in contact with theclosely wound portion 3 a, and a reliable contact between the stemportion 2 c and closely wound portion 3 a can be ensured at the time oftesting as shown in FIG. 2. The electric signal I is conducted axiallythrough the electroconductive needle member 2, and then to the closelywound portion 3 a. As can be readily appreciated, the electric signalcan flow axially through the closely wound portion 3 a of thecompression coil spring 3, instead of along a spiral path, so that theinductance of the electroconductive contact unit 1 can be effectivelyminimized.

[0029] In this electroconductive contact unit 1, as shown in FIG. 3, theentire surface of the electroconductive needle member 2 is formed with agold plated layer 8 via a Ni under layer 7 a, and the needle portion 2 ais additionally formed with an iridium layer 9 via a Ni under layer 7 bon top of the gold plated layer 8. The Ni under layer 7 a improves theattachment of the gold plated layer 8. The iridium layer 9 may consistof either iridium or an iridium alloy.

[0030] An example of the structures of the various layers is given inthe following. The needle member 2 including the needle portion 2 a,flange portion 2 b, stem portion 2 c and enlarged diameter portion 2 dall in a coaxial arrangement is generally Ni plated so as to form a Niunder layer 7 a, and is gold plated thereon to form a gold plated layer8 which is highly electroconductive and wear resistant.

[0031] As shown in FIG. 4, the electroconductive needle member 2 formedwith the gold plated layer 8 is held by a fixture 10 at the base end(adjacent to the flange portion 2 b) of the needle portion 2 a. A Niunder layer 7 b having a thickness of 1 μm or less is formed on the partof the needle portion 2 a exposed from the fixture 10, and the needleportion 2 a still held by the fixture 10 is exposed to an Ir target 11so that sputtering may be conducted thereon from above and sideways.Iridium (or an alloy thereof) which is resistant to oxidization, wearresistant and electroconductive is thus sputtered over the entiresurface of the needle portion 2 a so as to form an iridium layer 9having a thickness of approximately 0.5 μm or less. The needle portion 2a is held by the fixture 10 by clamping as illustrated in FIG. 4, butmay also by hooking the flange portion 2 b onto a fixture, and theorientation of the needle portion may also be horizontal or inverted asdesired.

[0032] Iridium was used in the illustrated embodiment, but the presentinvention is not limited by this selection of the material, and thereare other materials that can achieve a similar result such as titaniumnitride (TiN), rhodium (Rh) and hafnium nitride (HfN). A titaniumnitride layer can be formed simply by replacing the iridium target ofthe foregoing embodiment with a titanium nitride target. Rhodium may beused as a layer of an alloy of platinum and rhodium formed by sputteringa mixture of platinum and rhodium

[0033] In regard to titanium nitride, by sputtering both titaniumnitride and gold or platinum in a nitrogen environment, a layer of analloy of titanium nitride and gold or platinum can formed. Similarly, inregard to hafnium nitride, by sputtering both hafnium nitride and goldor platinum in a nitrogen environment, a layer of an alloy of hafniumnitride and gold or platinum can formed. The rhodium, titanium nitrideand hafnium nitride layers that can be used in place of the iridiumlayer 9 can provide a similar performance, and the tip of the needlemember 2 can be made electroconductive, resistant to oxidization andwear resistant.

[0034] According to this arrangement, it is possible to benefit from theadvantages of such materials as iridium, titanium nitride, rhodium andhafnium nitride. The advantages include high hardness, resistance toheat and acid, and a stable contact resistance. In particular, the wearresistance and durability of the tip of the needle portion 2 a can beimproved, and a conductance based on a highly stable mechanical contactcan be ensured (the contact resistance can be made stable). Because thealloy layer or metallic layer can be formed by plating or sputtering,the advantages of the present invention can be gained without modifyingthe existing shape of the electroconductive needle member, and thisprevents a rise in the manufacturing cost.

[0035] Because only the part that may wear or deform due to impacts andpressure is required to be processed for an increased hardness (such asthe formation of an iridium layer in the foregoing embodiment), theremaining part of the needle member may be coated with a highlyelectroconductive material such as a gold plated layer. For instance,because the enlarged diameter portion which is press fitted into thecompression coil spring is provided with a gold plated layer 8, thecontact resistance between the press fitted part of the compression coilspring and the needle member can be minimized. Therefore, even when apart of the electric signal I flows via the press fitted part of thecompression coil spring 3, the influence from the resulting contactresistance can be minimized.

[0036]FIG. 2 shows the way the electric signal I flows, and it can beseen that the electric signal I flows through the contact portionbetween the stem portion 2 c of the needle member 2 and the closelywound portion 3 a of the coil spring 3. In this case, the electricsignal flows through the needle member 2 mostly via the gold platedlayer 8 owing to the skin effect. The electric signal may be conductedby the iridium layer 9 at the tip of the needle portion 2 a, but becausethe gold plated layer 8 is formed in the lower layer of the needleportion 2 a the electric signal also flows through the gold plated layer8. In this manner, having the gold plated layer 8 formed over the entiresurface of the needle member 2 produces a highly desirable result. Also,the gold plated layer 8 on the stem portion 2 c is beneficial whensoldering the coil spring 3 thereto. The gold plated layer 8 ensures thecorrosion resistance of the needle member 2, and allows the material ofthe needle member 2 to be selected relatively freely without regard tothe electroconductivity or corrosion resistance thereof.

[0037] The Ni under layer 7 b was formed before forming the iridiumlayer 9 because iridium is resistant to oxidization and wear andelectroconductive but cannot be coated directly over the gold platedlayer 8 without difficulty. By the intervention of the Ni under layer 7,the coating strength (resistance to peeling) of iridium can besignificantly improved. The material for this under layer 7 is notlimited to Ni, but may also be others as long as they can improve theresistance of iridium against peeling.

[0038] When the iridium layer 9 was formed on the surface of the tip ofthe needle member 2, the diameter of the tip was approximately 5 μm orless after it was applied to a glass plate one million times and thewear of the iridium layer 9 was relatively insignificant. When theneedle member was only coated with a gold plated layer, the diameter ofthe tip was approximately 20 μm or more after it was applied to a glassplate one million times and the underlying metal was exposed.

[0039] The tip of the needle portion 2 a was provided with a pointedconical shape in the illustrated embodiment, but the shape is notlimited by this example. For instance, the tip may be formed as any ofthose illustrated in FIGS. 5a to 5 c. The one illustrated in FIG. 5a hasa conical shape having a rounded tip. The one illustrated in FIG. 5b isshaped as a combination of a plurality of prismatic shapes. The oneillustrated in FIG. 5c is provided with a blunt and flat end surface.The shape of the tip can be suitably selected according to the shape ofthe object to be contacted. For instance, the one illustrated in FIG. 5cis suitable for contact with a solder ball.

[0040] Furthermore, by orienting the sputtering direction as representedby arrow S in FIG. 5a, the iridium layer may be formed only on each ofthe faces 12 a, 12 b and 12 c (tip of the needle member) directed towardthe sputtering direction. In such a case, the iridium layer is formedonly on the surface that is to be contacted with an object to becontacted, and the material cost can be minimized.

[0041] In the foregoing embodiment, the electroconductive contact unithad only one end that is moveable. However, the present invention can beapplied to electroconductive contact units having two moveable ends, andthose using an electroconductive needle member that is supported as acantilever. In such a case, it suffices if at least the tip (the partthat comes into contact with the object to be contacted) of the needlemember is integrally provided with material which is resistant tooxidization and wear and electroconductive such as iridium.

[0042] As illustrated in FIG. 6, an additional gold plated layer 13 maybe formed on the surface of the iridium layer 9. In this arrangement,the iridium layer 9 provides the required resistance to wear and thegold plated layer 13 provides the corrosion resistance and low electricresistance, and an needle member providing an even more stable contactresistance can be achieved. Even when the gold plated layer 13 has wornout or deformed and the underlying iridium layer 9 is exposed, owing tothe gold plated layer 13 still remaining around the exposed portion, ahigh electric conductivity of the needle member 2 can be maintained as awhole.

[0043] In the illustrated embodiments, the gold plated layer 8 wasformed over the entire surface of the needle member 2, and the iridiumlayer 9 was formed only on the tip of the needle member 2 on top of thegold plated layer 8, but the gold plated layer 8 may be omitted from thepart where the iridium layer 9 is formed. In other words, the goldplated layer is required to be provided at least in the part (such asthe flange portion 2 b, enlarged diameter portion 2 d and stem portion 2c in the case of the illustrated embodiments) where the iridium layer 9is not formed.

[0044]FIG. 7 illustrates such an example. The embodiment illustrated inFIG. 7 is similar to that illustrated in FIG. 3, and the correspondingparts thereof are denoted with like numerals without repeating thedescription of such parts. As shown in the drawing, a Ni under layer 7 ais provided over the entire surface of the needle member 2, and aniridium layer 9 is formed on the needle portion 2 a. The part where theiridium layer 9 is absent (the flange portion 2 b, enlarged diameterportion 2 d and stem portion 2 c in the case of the illustratedembodiments) is formed with a gold plated layer 8. The order of formingthese two layers 8 and 9 can be freely selected, and a mask may be usedwhen forming each layer. In the case of the embodiment illustrated inFIG. 7, the electric signal flows first through the iridium layer 9 andthen through the gold plated layer 8. When this is applied to theembodiment illustrated in FIG. 6, the electric signal can transmit fromthe gold plated layer 13 to the gold plated layer 8, and the favorableelectric properties of gold can be even more fully taken advantage of.

[0045] Although the present invention has been described in terms ofpreferred embodiments thereof, it is obvious to a person skilled in theart that various alterations and modifications are possible withoutdeparting from the scope of the present invention which is set forth inthe appended claims.

Industrial Applicability

[0046] As can be appreciated from the foregoing embodiments, the tip ofthe needle member can be made highly resistant to oxidization and wear,and the wear resistance and durability of the electroconductive contactunit can be improved easily without using any special material for theneedle member. For instance, even when material such as iridium nothaving a favorable electric conductance is used, the resistance of theelectric path between the needle member and coil spring can be minimizedby plating at least the remaining part of the needle member withmaterial having a high electric conductivity. Therefore, the durabilityof the needle member is improved, and the running cost can be reduced.

[0047] In particular, by forming a gold plated layer over the entiresurface of the needle member, and additionally forming a layerconsisting of any of iridium, titanium nitride, rhodium and hafniumnitride either by itself or as an alloy with gold or platinum via anunder layer for preventing peeling, even when the needle member is madeof conventionally used material such as SK material, the gold platedlayer reduces the electric resistance of the electric path extendingfrom the tip of the needle member to the coil spring, and the underlayer permits the material such as iridium to be firmly attached to thegold plated layer. Thereby, the favorable properties of the materialsuch as iridium can be given to the needle member. The favorableproperties include high hardness, resistance to heat and acid and astable contact resistance. The gold plated layer provides a highelectric conductivity in a stable manner.

[0048] By forming a gold plated layer on top of the layer of materialsuch as iridium, the wear resistance can be increased owing to thematerial such as iridium, and a low electric resistance can be ensuredowing to the gold plated layer at the same time. In such a case, evenwhen the gold plated layer is worn or deformed and the underlying layermade of such material as iridium is exposed, the presence of the goldplated layer adjacent to such an exposed part helps the electricconductivity of the needle member as a whole to be kept high.

1. An electroconductive contact unit including an electroconductive needle member, and a coil spring resiliently urging the needle member in a direction to bring a tip portion of the needle member into contact with an object to be contacted, characterized by that: the tip portion of the needle member is integrally formed with electroconductive material resistant to oxidization and wear.
 2. An electroconductive contact unit according to claim 1, wherein at least a part of the needle member that is not integrally formed with the electroconductive material is plated with highly electroconductive material.
 3. An electroconductive contact unit according to claim 1, wherein the electroconductive material consists of any of iridium, titanium nitride, rhodium and hafnium nitride either by itself or as an alloy with gold or platinum.
 4. An electroconductive contact unit according to claim 3, wherein the iridium, titanium nitride, rhodium, hafnium nitride or alloy of any one of them with gold or platinum is provided via an under layer for preventing peeling.
 5. An electroconductive contact unit according to claim 2, wherein the electroconductive material consists of any of iridium, titanium nitride, rhodium and hafnium nitride either by itself or as an alloy with gold or platinum.
 6. An electroconductive contact unit according to claim 5, wherein the iridium, titanium nitride, rhodium, hafnium nitride or alloy of any one of them with gold or platinum is provided via an under layer for preventing peeling.
 7. An electroconductive contact unit according to claim 2, wherein the highly electroconductive material that is plated consists of gold.
 8. An electroconductive contact unit according to claim 7, wherein the electroconductive material consists of any of iridium, titanium nitride, rhodium and hafnium nitride either by itself or as an alloy with gold or platinum.
 9. An electroconductive contact unit according to claim 8, wherein the gold plating is formed over the entire surface of the needle member, and the iridium, titanium nitride, rhodium, hafnium nitride or alloy of any one of them with gold or platinum is provided via an under layer for preventing peeling.
 10. An electroconductive contact unit according to claim 9, wherein a gold plating is formed on top of the iridium, titanium nitride, rhodium, hafnium nitride or alloy of any one of them with gold or platinum. 